Conventional video displays (e.g., televisions, monitors, etc.) can include a cathode ray tube (CRT). CRT displays generally present a picture or video image via a raster created by horizontal and vertical scanning of an electron beam. Although the exact number of scans per second and the methods of scanning can vary, the basic scanning arrangement is almost universally implemented. The image on a CRT display is formed by fine lines that are generated by moving the electron beam rapidly from left to right and back to left, while simultaneously moving the electron beam gradually downward. When the electron beam reaches the bottom of the screen, the beam returns to the top of the screen. The left-to-right and downward motions occur with the electron beam controlled by picture or video information, while the right-to-left motion (e.g., horizontal retrace, or flyback) and the vertical motion (e.g., vertical retrace), are performed with the electron beam off (or blanked).
Referring to FIG. 1, a diagram illustrating an analog video signal 10 is shown. The analog video signal 10 has an active portion and an inactive portion. The active portion contains the picture information (or image) to be displayed (e.g., visible lines). The inactive portion generally does not contain any video information. The inactive portion generally includes synchronization and blanking information (e.g., horizontal and vertical) that allows the electron gun to perform the horizontal and vertical retraces. For example, the inactive portion of the analog video signal 10 has a vertical blanking period 12 (for each field in an interlaced image or frame in a non-interlaced image) and a horizontal blanking period 14 (for each field/frame line).
Referring to FIG. 2, a diagram illustrating a video image 20 is shown. The video image 20 has an active region (or area) 22. The remainder of the image 20 is an inactive region (or area). When a digital video signal is to be converted to an analog video signal, the digital signal generally comprises the entire picture to be presented, including the horizontal and vertical blanking intervals (i.e., the inactive area).
In conventional systems, a portion of the active region 22 of the video image 20 is overscan. The overscan portion allows the image 20 to fill the entire viewable area (e.g., on consumer monitors and televisions). The overscan portion can contain actual image data. However, the overscan portion generally falls outside the viewable area of the screen.
When a digital video decoder is connected to a video digital-to-analog converter (DAC), the signal exchanged between the two devices is a sampled version of the entire picture (i.e., luminance (Y) and chrominance (Cr and Cb) components interleaved) The sampling rate (i.e., samples/line) as well as the number of active and inactive lines typically conform to a predefined standard (e.g., NTSC, PAL, etc.) that allows for interoperability of various devices.
Standard scanning formats currently in use include standard-definition (SD) video signals (i.e., 480i, where i indicates a frame comprises two interlaced fields) and high-definition (HD) video signals (i.e., 1080i and 720p, where p indicates a progressive scan or non-interlaced image). The number of high-definition television (HDTV) sets is growing. However, a large installed base of standard definition (SD) equipment is still available.
It would be desirable to have an apparatus and/or method for simultaneous display of video at two resolutions with different fractions of active regions.